The present invention relates to a swing-type actuator such as an actuator for magnetic disk drives, and more particularly to a swing-type actuator capable of swinging a function member such as a magnetic head along a circular course.
Conventionally, the positioning of a magnetic head on a recording track of a magnetic disk, etc. is conducted by a swing-type or rotation-type actuator as shown in FIGS. 9 and 10. In both figures, a yoke 1 is fixedly provided with permanent magnets 2, and a pair of yokes 1 are assembled by supports 3 such that different magnetic poles of the permanent magnets 2 are opposite each other via a magnetic gap 4 to form a magnetic circuit. 5 represents an arm having one end to which a flat movable coil 6 is fixed, and the other end to which a magnetic head (not shown) is fixed. The arm 5 is arranged such that the movable coil 6 located in the magnetic gap 4 can swing around a shaft 7.
When an operation signal is supplied to the movable coil 6, a magnetic force generated from the movable coil 6 according to Fleming's left hand rule functions as an attraction force or a repulsion force to each permanent magnet 2, so that the arm 5 is rotated around the shaft 7. As a result, a magnetic head fixed to a tip end of the arm 5 is positioned on a desired magnetic track of a magnetic disk (not shown). The direction of the rotation of the arm 5 can be changed by inverting the direction of current applied to the movable coil 6.
In the above conventional actuator for magnetic disk drives, the movable coil 6 is usually fixed to the arm 5 by an adhesive. However, the fixing of the movable coil 6 by an adhesive is sometimes troublesome, failing to provide accurate positioning of the movable coil 6. In addition, handling of terminals of the movable coil 6 is complicated, lowering the efficiency of assembling of the arm 5. Since there is increasingly higher demand for miniaturization and reduction in thickness of magnetic disk drives, it is necessary to improve the positioning accuracy of the movable coil 6, and the efficiency and reliability of fixing of the movable coil 6 to the actuator 5. In this sense, the conventional arms fail to satisfy these requirements.
To solve the above problems, attempts have been made to integrally fix a movable coil 6 to an arm 5 by an integral resin molding (for instance, U.S. Pat. No. 4,855,853 and Japanese Utility Model Laid-Open No. 60-159566). In such a structure, the movable coil can be supported by a simplified structure, and the thickness of the movable coil can be extremely reduced. Accordingly, such a structure is advantageous for miniaturizing actuators.
However, in the above resin-molded structures, the actuator does not have sufficient mechanical strength, particularly resistance to detachment and bending strength, and the fixing of the arm 5 to the movable coil 6 is insufficient. Particularly, when the periphery of the arm 5 on the side of the movable coil 6 is circular or in a curved shape, or when the arm 5 has a narrow bonding area, it is difficult for the actuator to have sufficient strength.
Also, since the movable coil 6 is embedded in a molding, there are resin layers on both sides of the movable coil 6, leading to a thicker actuator. If such a thick actuator is used, the magnetic gap 4 should be enlarged. Accordingly, the magnetic properties of the permanent magnets 2 cannot be fully utilized, so that the actuator fails to exhibit sufficient performance and driving power.